Reduction of scale in steam boilers



United States Patent REDUCTION OF SCALE IN STEAM BOILERS Myron J. Jursich, Chicago, 111., assignor to National Aluniinate Corporation, Chicago, Ill., a corporation of Delaware No Drawing. Application October 2, 1951, I

Serial No. 249,407

17 Claims. (Cl. 210-23) This invention relates to the reduction and prevention of scale in steam boilers.

In steam boilers where water is boiled at superatmospheric pressures to generate steam one of the more troublesome problems encountered has been the tendency of the water containing any hardness to deposit this hardness as scale on the heat exchanging surfaces. The scale reduces the heat transfer across the heat exchanging surface so that there is an increased tendency for the metal to overheat. This can and often does lead to rupture of boiler heat exchange surfaces. Present boiler scale reduction practice is to employ compounds such as tannins, modified lignins, algins and other complex organic compounds to prevent the formation of scale on the metal surfaces. The employment of these compounds has one or more of the following disadvantages: (1) oxidation in the boiler; (2) decomposition on the metal surface with deposition of carbon on the metal and failure due to overheating in high pressure boilers; (3) the requirement of relatively large amounts to inhibit scale; (4) certain types of scale, such as magnesium phosphate, are unaffected by conventional types of organic compounds; and (5) conventional boiler scale inhibitors are highly colored so that steam that is contaminated by carryover cannot be used for food processing or other purposes where color and contamination are factors.

One of the objects of the present invention is to provide a boiler scale treatment which avoids many of the disadvantages of previously used treatments.

Another object is to provide new and useful boiler scale reducing compositions which have a wide range of application. Other objects will appear hereinafter.

It has now been found in accordance with the present invention that polymers of nitrophenols which have 'a nitro group orthoto the phenolic hydroxy group are very effective in preventing the formation of calcium carbonate scale at relatively low superatmospheric steam pressures and of calcium and magnesium phosphate scale at relatively high superatmospheric steam pressures. The polymers employed for the purpose of the invention may be in the form of dimers, trimers, tetramers and can have a higher state of polymerization provided they are substantially soluble in alkaline aqueous solutions. If the polymer does not contain a nitro group orthoto the phenolic hydroxy group, the desired result is not obtained.

As an illustration, a dimer suitable for the practice of the invention is obtained by condensing one mol of formaldehyde with two mols of phenol and then nitrating to produce a product having the following formula OH H -on NO: NO:

Any alkali soluble polymer may be employed containing two or more orthonitrophenol nuclei linearly attached di- 2,749,305 Patented June 5, 19 56.

rectly to each other (e. g., as in dior tri-(nitrohydroxyphenyl) derivatives) or through a hydrocarbon chain (e. g., as in the dior tri-(nitrohydroxy'phenyl) methanes, the di-, or tri-(nitrohydroxyphenyl) ethanes, the dior tri- (nitrohydroxyphenyl) propanes, and homologues in which two or more nitrophenol nuclei are connected linearly by an acyclic aliphatic hydrocarbon group).

In the practice of the invention the orthonitrophenol polymer, either as such or in the form of a water soluble salt, can be added to the boiler feed water or directly to the water in the boiler where the steam is generated.

The boiler water from which the steam is generated preferably has a pH within the range of 9 to 11.

The invention will be illustrated but is not limited by the following examples showing the manner in which polymers suitable for the practice of the invention are prepared and how they are employed for the purpose of the invention.

Example I with grams of water and 3 cc. of concentrated sulfuric acid. 17 grams (.22 mol) formalin (40%) was then added. The mixture was refluxed for two hours. At the end of this time a clear viscous layer formed on the bottom of the flask. On cooling, the layer solidified and the aqueous portion was decanted. The product was dissolved in 150 cc. of 10% sodium hydroxide and the small insoluble portion filtered off. The alkaline solution was diluted with water and the product precipitated by making the solution acid with hydrochloric acid. The water was decanted and the product dried under vacuum. The polymer obtained softened just below 100 C.

21.4 grams of this polymer was dissolved into 42.8 grams of glacial acetic acid. This mixture was added dropwise with stirring to a cold mixture of 60 cc. concentrated nitric acid and 30 cc. glacial acetic acid. The addition was controlled at such a rate as to keep the temperature below -1 C. Stirring was continued for /2 hour longer after the addition was complete. The nitrated mixture was poured on crushed ice, filtered, and then washed with 400 cc. of 5% sodium bicarbonate. The product was filtered, slurried with methanol, filtered and dried. 28 grams of a yellow powder was obtained.

The polymer prepared as above described was used in boiler scale tests :and when added to the boiler feed water in the proportion of 0.5 grain per gallon of boiler feed water gave a 40% reduction in carbonate scale formation in a low pressure steam boiler operating at 250 p. s. i. When used in proportions of 2.0 grains per gallon of boiler feed water this polymer gave 95% scale reduction under the same operating conditions.

Example 11 21.4 grams of 6,6'-dihydroxy-3,3'-dimethyldiphenylmethane Was dissolved in 21.4 grams of acetic acid. This was added with stirring to a solution of 30 cc. glacial acetic acid and 60 cc. of concentrated nitric acid. The temperature was maintained at l C. during the course of the addition and for one hour longer. The mixture was poured onto crushed ice and filtered. The filter cake was washed with 5% sodium bicarbonate solution and dried. 17 grams of a yellow powder, 6,6-dihydroxy-5,5- dinitro-3,3'-dimethyldiphenylmethane, was obtained.

At a dosage of 2 grains per gallon of boiler feed Water the foregoing polymer produced a carbonate scale reduction of in a steam boiler operating at 250 p. s. i.

Example III Example II to produce 2,6-di(2 hydroxy-3-nitro-5-methylbenzylr) p-cresol.

At a dosage of 2 grains per gallon of boiler feed water in a steam boiler operating at 250 p. s. i. this polymer gave a carbonate scale reduction of 90%. At the same dosage in a steam boiler operating at 1500 p. s. i. this polymer gave a calcium phosphate scale reduction of 65%.

Example IV 22 parts of 6,6-dihydroxy-3,3'-diethyldiphenylmethane were nitrated in the same manner as in Example II. 25 grams of a yellow powder, 3,3'-diethyl-6,6'-dihydroxy- 5,5'dinitrodiphenylmethanc, were obtained.

At a dosage of 2 grains per gallonv of boiler feed water in a. steam boiler operating at 250 p. s. -i. this polymer produced a. carbonate scale reduction of about 50%.

Example V 50 cc. ofiglacial acetic acid and 60 cc. of concentrated nitric-acid were mixed and cooled to -l5 C. While stirring the cooled mixture 22 grams (.12 mol) of p,pdihydroxybiphenyl were added slowly as the solid powder at such a rate as to maintain the temperature at l5 C. The mixture was stirred for one additional hour and poured onto crushed ice. The product was filtered, washed with dilute sodium bicarbonate and water and then dried. 27.5 grams of a brown powder, 4,4dihydroxy-B,3-dinitrobiphenyl, were obtained.

At a dosage of 2 grains per gallon of boiler feed water in a steam boiler operating at 250 p. s. i. this polymer gave an 80% reduction in the formation of carbonate scale.

Example VI The procedure was the same as that employed in Example II except that the following reactants were employed:

22' grams 3,3 diethyl 6,6-dihydroxy-n-propyldiphenyl methane 52 cc. glacial acetic acid 60 cc. concentrated nitric acid The resultant product was 3,3'-diethyl6,6-dihydroxy- 5,5-dinitro-n-propyldiphenylmethanc.

At a dosage of 2 grains per gallon of boiler feed water in a steam boiler operating at 250 p. s. i. this polymer produced about 20% reduction in the formation of carbonate scale.

Example VII The procedure used in preparing the polymer was the same as that employed in Example H except that the following reactants were employed:

2.2 grams 2,2-dihydroxy-5,5'-dimethyl-n-propyldiphenylmethane 44 cc. glacial acetic acid 60 cc. concentrated nitric acid The product was 2,2-dihydroxy-3,3-dinitro-5,5-dimethyl-n-propyldiphenylrnethane.

At a dosage of 2 grains per gallon of boiler feed water in a steam boiler operating at 250 p. s. i. this polymer produced about a 40% reduction in carbonate scale formation.

Example VIII The procedure was the same as in Example H except that the following reactants were employed:

40 grams 4,4'-dihydroxy-a,a-dimethyldiphenylmethane 60 grams glacial acetic acid 120 ml. nitric acid The product was 4,4'-dihydroxy-3,3,5,5'-tetranitrodiphenyl-a,a-dimethylrnethane.

At a dosage of 2 grains per gallon of boiler feed water in a steam boiler operating at 250 p. s. i. this polymer reduced the formation of. carbonate scale 25% Example IX The procedure was the same as described in Example II except that the reactants were as follows:

8.2 grams 2,2,6,6-tetrahydroxy-diphenylmethane 45 grams glacial acetic acid 30 grams nitric acid The product is a mixture of nitro derivatives of tetrahydroxydiphenylmethane.

At a dosage of 2 grains per gallon of feed water in a steam boiler operating at 250 p. s. i. this polymer produced a reduction in carbonate scale formation.

For the tests at 250 p. s. i. a dilute Hinsdale, Illinois water was used (Ca hardness=9 grains per gallon, magnesium hardness=5 grains per gallon, M=10.5) which was treated with NaHCOs to give an alkalinity of 25 grains per gallon in the boiler at 10 concentrations. Fifty gallons of this water were evaporated in an inclined tube boiler of the type described by Holmes and Jacklin Experimental Studies of Boiler Scale at 800 P. S. I." reported in Proceedings of Fourth Annual Water Conference, November 1-2, 1943, and Experimental Studies of Boiler Scale at 1500 P. S. I. reported in Proceedings of Sixth Annual Water Conference, October 22-23, 1945. The orthonitrophenol polymer was added to the feed water in the quantifies described in the examples. As will be apparent to those skilled in the art, the water used produces carbonate scale and scaling is inhibited by the orthornitrophenol polymer.

In the tests at 1500 p. s. i. the water used contained 1 grain per gallon of calcium and was treated with NaHCOa and NazHPO; to give an alkalinity of 20 grains per gallon (g. p. g.) and a P04 concentration of 50 parts per million (p. p. m.) in the boiler water at 10 concentrations. Fifty gallons of this water were evaporated in a horizontal tube boiler and the orthonitrophenol polymer was added to the feed water in the amounts previously mentioned.

The quantity of the orthonitrophenol polymer employed for the purpose of the invention may be varied but effective results are usually obtained by adding 0.5 to 2.0 grains of the polymer per gallon of boiler feed water.

The orthonitrophenol polymers employed in accordance with the present invention are effective in reducing and preventing scale in low pressure boilers to 500 pounds per square inch steam pressure), high pressure boilers (1000 to 1500 pounds per square inch steam pres sure) and intermediate pressure boliers (500 to 1000 pounds per square inch steam pressure), but the effectiveness willvary somewhat depending upon the type of scale encountered in the boiler operation. The polymers em ployed in the practice of the present invention are particularly useful in preventing carbonate scale in low pressure steam boilers. Although calcium carbonate and calcium phosphate scales are most often encountered com: mercially, other types of scales such as calcium silicate, magnesium hydroxide and magnesium phosphate scales are inhibited by the practice of the invention.

The invention is hereby claimed as follows:

1. A method of reducing scale in boilers in the generation of steam from water which tends to form a scale which comprises incorporating with said water from which the steam is generated a quantity of an orthonitrophenol polymer effective to reduce scale formation, said polymer having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other and said polymer being soluble in alkaline aqueous solu tions having a pH within the range of 9 to 11, and boiling said water.

2. A method of reducing scale in boilers in the generation of steam from water which tends to form a scale which comprises incorporating with said water from which the steam is generated a quantity of an orthonitrophenol polymer effective to reduce scale formation, said polymer having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other and said polymer being soluble in alkaline aqueous solutions having a pH within the range of 9 to 11, and boiling said water under superatmospheric pressure conditions.

3. A method of reducing scale in boilers in which steam is generated from water which tends to form a scale which comprises incorporating with said water from which said steam is generated and which has a tendency to form calcium carbonate scale in the boiler during steam generation a quantity of an orthonitrophenol polymer sufiicient to reduce said scale formation, said polymer having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other and said polymer being soluble in alkaline aqueous solutions having a pH within the range of 9 to 11 and boiling said water.

4. A method of reducing scale in boilers in which steam is generated from water which tends to form a scale which comprises incorporating with said water from which said steam is generated and which has a tendency to form calcium phosphate scale in the boiler during steam generation a quantity of an orthonitrophenol polymer suflicient to reduce said scale formation, said polymer having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other and said polymer being soluble in alkaline aqueous solutions having a pH within the range of 9 to 11 and boiling said water.

5. A process as claimed in claim 1 in which said polymer is a nitrated product of the reaction of phenol and formaldehyde having nitro groups orthoto phenolic hydroxy groups in the phenyl nuclei.

6. A process as claimed in claim 1 in which said polymer is 6,6'-dihydroxy-5,5'-dinitro-3,3'-dimethyldiphenylmethane.

7. A process as claimed in claim 1 in which said polymer is 2,6-di(2-hydroxy-3-nitro-S-methylbenzyl-)p-cresol.

8. A process as claimed in claim 1 in which said polymer is 4,4'-dihydroxy-3,3'-dinitrobiphenyl.

9. A process as claimed in claim 1 in which said polymer is a mixture of nitrotetrahydroxydiphenylmethanes.

10. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and containing an orthonitrophenol polymer dissolved therein in a quantity sufficient to inhibit scale formation when steam is generated from said water under superatmospheric pressure conditions, said polymer having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other.

11. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form calcium carbonate scale when steam is generated by boiling said water, said boiler water containing a quantity of an orthonitrophenol polymer suflicient to reduce said carbonate scale formation, said polymer being soluble in said boiler water and having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other.

12. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form calcium phosphate scale when steam is generated by boiling said water, said boiler water containing a quantity of an orthonitrophenol polymer sufficient to reduce said carbonate scale formation, said polymer being soluble in said boiler water and having recurring phenyl nuclei each containing a hydroxyl group and a nitro group in positions ortho to each other.

13. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form scale when steam is generated therefrom, said boiler water containing a quantity of a polymer which is a nitrated product of the reaction of phenol and formaldehyde having nitro groups orthoto phenolic hydroxy groups in the phenyl nuclei and which is soluble in said boiler water, the quantity of said polymer being effective to reduce said scale formation when steam is generated from said boiler water under superatmospheric pressure conditions.

14. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form scale when steam is generated therefrom, said boiler water containing a quantity of 6,6'-dihydroxy-5,5'-dinitro-3,3'-dimethyldiphenylmethane, the quantity of said polymer being effective to reduce said scale formation when steam is generated from said boiler water under superatmospheric pressure conditions.

15. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form scale when steam is generated therefrom, said boiler water containing a quantity of 2,6-di(2-hydroxy-3-nitro-5-methylbenzyl-)pcresol, the quantity of said polymer being effective to reduce said scale formation when steam is generated from said boiler water under superatmospheric pressure conditions.

16. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form scale when steam is generated therefrom, said boiler water containing a quantity of 4,4'-dihydroxy-3,3'-dinitrobiphenyl, the quantity of said polymer being effective to reduce said scale formation when steam is generated from said boiler water under superatmospheric pressure conditions.

17. A process of generating steam which comprises boiling a boiler water having a pH within the range of about 9 to 11 and having a tendency to form scale when steam is generated therefrom, said boiler water containing a quantity of a mixture of nitrotetrahydroxydiphenylmethanes containing hydroxyl groups and nitro groups ortho to each other in the phenyl nuclei, the quantity of said mixture being effective to reduce said scale formation when steam is generated from said boiler water under superatmospheric pressure conditions.

References Cited in the file of this patent UNITED STATES PATENTS 2,029,960 Urbain Feb. 4, 1936 FOREIGN PATENTS 573,522 Germany July 8, 1923 642,238 Great Britain Aug. 30, 1950 

1. A METHOD OF REDUCING SCALE IN BOILERS IN THE GENERATION OF STEAM FROM WATER WHICH TENDS TO FORM A SCALE WHICH COMPRISES INCORPORATING WITH SAID WATER FROM WHICH THE STEAM IS GENERATED A QUANTITY OF AN ORTHONITROPHENOL POLYMER EFFECTIVE TO REDUCE SCALE FORMATION, SAID POLYMER HAVING RECURRING PHENYL NUCLEI EACH CONTAINING A HYDROXYL GROUP AND A NITRO GROUP IN POSITIONS ORTHO TO EACH OTHER AND SAID POLYMER BEING SOLUBLE IN ALKALINE AQUEOUS SOLUTIONS HAVING A PH WITHIN THE RANGE OF 9 TO 11, AND BOILING SAID WATER. 